In recent years, a technique for forming a thin film transistor (TFT) using a semiconductor thin film (with a thickness of approximately several to several hundreds nm) which is formed over a substrate having an insulating surface has attracted attention. The thin film transistor is widely applied to an electronic device such as an electro-optical device or an IC, and has been hurriedly developed particularly as a switching element of a liquid crystal display device.
In a liquid crystal display device used for a notebook personal computer or a cellular phone, a large number of pixels are formed by sandwiching a liquid crystal material between a pair of light-transmitting substrates at least one of which is provided with a transparent electrode, and each pixel is provided with a switching element which selects an electrode. The liquid crystal display device performs display by selecting the switching element, performing optical switching of liquid crystal molecules by voltage application, and turning on and off each pixel.
In a liquid crystal display device, liquid crystal molecules need to be uniformly aligned in order to improve display characteristics. Liquid crystal alignment treatment of an alignment film provided to uniformly align liquid crystal molecules includes alignment treatment called rubbing and alignment treatment by light irradiation.
The alignment treatment by rubbing is a method of forming an alignment film over a substrate and then rubbing a surface of the alignment film with nylon, rayon, or the like, and is widely used for manufacturing of liquid crystal display devices. However, since rubbing is a method of directly rubbing an alignment film with cloth, it has problems of static electricity generation and dust generation by scraping the alignment film. The static electricity generation may result in destruction of a switching element formed over a substrate.
In the alignment treatment by light irradiation, it is necessary to form an alignment film using a special material and make irradiation light obliquely incident on a surface of the alignment film in order to form a pretilt angle. Therefore, it is difficult to uniform irradiation light energy with respect to a surface of a substrate, and a pretilt angle may become uneven.
In a TN mode liquid crystal display, rubbing treatment using light irradiation or cloth is required after forming an alignment film. Thus, a vertical alignment (VA) mode liquid crystal display which performs liquid crystal alignment using a rib structure or a technique of alignment division has attracted attention.
An example of the VA (Vertical Alignment) mode is a PVA (Patterned Vertical Alignment) mode, an MVA (Multi-domain Vertical Alignment) mode, or the like.
In addition, Reference 1 discloses that liquid crystal is vertically aligned by a technique using as an alignment film a self-assembled monolayer obtained by applying a solution of a silane compound suspended in a solvent over a transparent conductive layer and baked to remove the solvent (Reference 1: Japanese Published Patent Application No. 2002-23169).